The invention relates to a method for heating an end section of a plastic pipe according to the preamble of claim 1 as well as a device for performing the corresponding method.
Plastic pipes produced by a continuous method are usually divided into certain lengths for storage, shipping and use. In sewer technology in particular, a number of different pipe lengths are assembled in a suitable manner to form pipelines at the construction site. One end of a pipe is provided with a sleeve into which the spigot end of another pipe can be inserted.
To produce a sleeve on a pipe, the corresponding end of the pipe is usually heated first to the deformation temperature and then the sleeve is shaped using a molding tool.
For heating the end section of a plastic pipe to the deformation temperature, it is known that the end section can be contacted by means of external heating jaws and the interior of the end section can be heated by a heating mandrel in a noncontact process. To compensate for manufacturing tolerances, a gap is usually provided between the heating mandrel and the interior wall of the pipe. Heat is transferred by means of radiant heat here. It is also known that the interior of the pipe can be heated by hot air.
It is known from DE 25 36 306 B2 that the end sections of a pipe can be heated by means of an infrared lamp, which is cooled by a stream of air during this heating. A similar design can also be found in EP 1 315 604 B1, in which several radiant heating elements are arranged eccentrically on a carrier that can be driven to rotate about the axis of the pipe, while gas jets assigned to them cool the interior of the plastic pipe at the site of the greatest thermal radiation. This cooling is necessary because high-energy input into the interior of the pipe is necessary to shorten the heating time, on the one hand, but, on the other hand, radiant heating without cooling the interior of the pipe would result in excessive surface temperatures. Instead of a radiant heating element, contact heating elements, which are designed as spreading mandrels, are also known but they are complex to manufacture and operate.
Another problem in heating plastic pipes is that there is a certain shrinkage of the diameter at the cut edge of a pipe, in particular when it is made of high-shrinkage plastics, such as polypropylene, polyethylene or PVC. When the end section of a pipe is heated by means of external heating jaws in contact with the pipe, there is no direct contact there because of the shrinkage of the end region of the pipe, so that adequate heating is not achieved on the exterior in the end region of the pipe. As a result, the dimensional stability may be impaired in subsequent production of the sleeve at the end of the pipe. At a construction site, when connecting the spigot end of one pipe with a maximum diameter by inserting it into a sleeve, it is often necessary to discard such pipes as not fitting.
Storage at an elevated temperature may also result in shrinkage in the end region of the pipe before beading and may make the pipe difficult to connect.
The object of the present invention is therefore to provide a method for heating an end section of a plastic pipe to prepare for the formation of a sleeve such that complete heating of the end section of the pipe up to the cut edge is possible. In addition, the invention is based on the object of providing a device for carrying out a corresponding method.